The various embodiments of the invention are related to electronic instrument amplifiers and more particularly to those that use digital techniques to emulate the generation of multiple simultaneous musical performances, e.g. double tracking.
In recording studios, the sound of a musical instrument is fattened or enhanced by over-dubbing several times the same part played using the instrument. Every instance of the performance differs from the others by subtle shifts in timing and tone. The blending of the different takes of the same musical part leads to some random chorusing and fluttering which makes for the sought-after character of this effect. One possible variation of this chorus technique is called double tracking in which only two takes of the performance are combined. Each take can receive independent processing such as distortion, filtering, etc., and the pair is then placed symmetrically in the stereo imaging space.
In contrast to the recording studio, double tracking in a live performance situation typically requires two performers playing the same musical part. That is because over-dubbing is not practical in a live performance. A more practical solution may be to use an electronic chorus generation system. For example, U.S. Pat. No. 4,369,336 describes how a chorus effect is formed, by a pair of complementary digital signals based on an original, analog audio signal. Another system is described in U.S. Pat. No. 4,384,505, where a string chorus generator accepts a single audio input signal, applies it to three separate delay lines, and provides delay modulated outputs to produce an ensemble musical effect resembling a group of strings in a string orchestra.